A patient receiving breath pressure support from a ventilator system typically receives breathing gas through a patient circuit of the ventilator. The patient circuit generally includes two conduits (e.g. flexible tubing) connected to a fitting referred to as a tubing circuit wye. The free ends of the conduits are attached to the ventilator so that one conduit receives breathing gas from the ventilator's pneumatic system, and the other conduit returns gas exhaled by the patient to the ventilator. The volume of the exhaled gas may then be measured before it finally exits through an exhalation valve. The wye fitting is typically connected to the patient's breathing attachment or enclosure, which conducts breathing gas into the lungs, and exhaled gas from the lungs to the exhalation branch of the patient circuit. The pneumatic system at the inhalation end of the patient circuit is typically closed before a breath, and the exhalation valve at the exhalation end of the patient circuit is typically preceded by a one-way valve, to prevent gas from flowing in the exhalation branch of the patient circuit.
During ventilation of a patient, it may be important to monitor the state of the gas path ways as these are the conduits of the gases delivered to and received from the patient. The flow of the therapeutic gases to and from the patient can be interrupted via different mechanisms, some related to the valves in the system or by blockage of the tubing system or by disconnections of the gas path way at any of the Ventilator's Breathing System (VBS) elements' interconnection points. In particular, the disconnection type of gas flow interruption is what ventilator designers refer to as “tubing circuit disconnection”.
Disconnections in the VBS are common occurrence during ventilation of patients. They can be caused by involuntary actions of the patient or the caregivers or the deliberate action of the care giver such as when suctioning of the patient airways is performed. When a VBS disconnection occurs, gas delivery to the patient is impaired and protection for the caregiver from airborne pathogens is usually impaired as well. Some disconnection episodes are more severe than others in particular when an accidental disconnection occurs (typically caused by involuntary patient action) and is not promptly identified by the ventilator thus the proper alarm is not issued, causing the patient to lack adequate ventilation from being delivered to his/her lungs. Disconnections can occur at several places in the VBS. A typical disconnection is that in which the patient's endotracheal tube (ET) or tracheotomy tube is separated from the tubing system patient port. Another type of disconnection is that that occurs when the tubing system is separated from the ventilator's exhalation port inlet. Furthermore, disconnections may occur at the water traps' or bacteria filter's connection ports or the humidifier etc. Also, the patient may become disconnected from his/her endotracheal tube or tracheotomy tube, which is typically referred to as extubation.
There may be a number of approaches, which are based on identification of conditions, particular to the pressures, delivered and exhaled flows and volumes that exist during a Ventilator's Breathing System disconnection episode. These approaches typically include a set of conditions for the system pressures and or flows and or volumes. In particular, in various known approaches, the pressure and flow criteria need to be chosen based on experimental data which is machine dependent. Such approaches are complex and require the determination of thresholds which can be machine dependent. Review of clinical literature with respect to this issue will readily indicate the frequency and potential hazard to the patient created by disconnections and their affect on the patient when not detected or when the approaches used are flawed or take a significant amount of time to detect these events.
Accordingly, it may be desired to provide for the reliable machine-independent approach for determination of patient disconnection in a ventilation breathing system.